Two salt forms of a fluoroquinolone antibacterial drug, ciprofloxacin (CIP), with non-steroidal anti-inflammatory drugs, diflunisal (CIP/DIF) and indoprofen (CIP/INDP/H2O), were synthesized and characterized by PXRD, FTIR, DSC, TGA and HSM. Crystal structure determination allowed us to study the drug–drug interactions and the piperazine-based synthon (protonated piperazinecarboxylate) in the two forms, which is potentially useful for the crystal engineering of new salt forms of many piperazine-based drugs.
